We have studied dielectric breakdown characteristics of this (approx. 10nm) silicon dioxide films grown on silicon under the following conditions: (A) Standard oxidation process with the oxides grown at 800C; (B) Annealing the oxides at 1000C in argon for 30 minutes after going through step (A); (C) Two - Step oxidation, i.e. 800C - 4 nm followed by 1000C anneal for 30 minutes in argon and a final oxidation, at 8000C to grow a total of 9 nm; (D) Growth of oxide at 1000C. The results show that (B) and (C) have comparable dielectric breakdown strengths, indicating that high temperature annealing has the same advantage as the two-step oxidation in improving the dielectric strength of silicon dioxide. High resolution transmission electron micrographs show that the interface structures are fairly similar in all the cases indicating that the interface smoothness as observed in the transmission electron micrographs are not directly responsible for the dielectric breakdown. Our observations of the protrusions at the Si/SiO2 interface may also possibly explain the high values of the refractive index which has earlier been attributed to a monolayer of non-stoichiometric SIOX at the SI/SiO2 interface.